Oil bodies (occasionally referred to as “lipid bodies”) are cell organelles that are present in large quantities in plants, and particularly in seed cells of oil crops. Oil bodies comprise a monolayer membrane of phospholipid comprising specific proteins referred to as oleosins, steroleosins, and caleosins, and they accumulate plant oil-and-fats in the form of triacylglycerol (TAG, neutral fat, or neutral lipid) therein. In particular, large quantities of plant oil-and-fats are accumulated in plant seeds. In the past, oil-and-fats accumulated in oil bodies have been analyzed by methods that involve pulverizing seeds to extract oil-and-fat components and performing gas chromatography, liquid chromatography, or other techniques. Such analytical methods, however, required the addition of lipid degradation inhibitors and processing at low temperatures. In addition, oil-and-fat components may be disadvantageously degraded.
Siloto, R. M. P. et al., Plant Cell 18, 1961-1974, 2006 discloses that oil body size is influenced by oleosin quantity. Wahlroos et al., GENESIS, 35 (2): 125-132, 2003 discloses that the oleosin gene is fused to the green fluorescent protein (GFP) gene and oil bodies, which are organelles in plant cells, can be observed with the aid of GFP fluorescence. Even if it is possible to observe oil bodies, however, the correlation between the number or form of oil bodies and the oil-and-fat amount or type accumulated in oil bodies has not yet been elucidated. In particular, the correlation between the form or number of oil bodies in cotyledons and the oil-and-fat amount in seeds has not yet been elucidated. During the growth process, a variety of reserved compounds, such as reserved starches, reserved proteins, and reserved oil-and-fats, are degraded and used in cotyledons while undergoing photosynthesis. Thus, it was considered to be difficult to deduce the oil-and-fat amount in seeds based on the form or number of oil bodies in cotyledons.